1. Field of the Invention
The present invention relates to a multi-input power converter and an uninterruptible power supply (UPS) having the same, and more particularly to a multi-input power converter that is constructed by multiple AC switches and raises the density of the input power, and an UPS having the multi-input power converter.
2. Description of Related Art
With reference to FIG. 10, which shows a conventional uninterruptible power supply (UPS) according to the prior art, comprises a power factor correction (PFC) and AC to DC converter (102), a DC to DC converter (104), a battery (105), a DC to AC inverter (106), an output filtering device (107) and a switch (103), wherein the switch (103) is electrically connected between the PFC and AC to DC converter (102) and the DC to DC converter (104). The switch (103) is turned off when utility power (101) is available, so the DC to DC converter (104) does not work. At this moment, the conventional UPS operates in so-called line mode. When the conventional UPS operates in the line mode, the PFC and AC to DC converter (102) converts the AC utility power (101) into DC power and outputs the DC power to the DC to AC converter (106) and the output filter (107) to convert the DC power into an AC output power. The AC output power is then provided to a load. On the contrary, when the utility power (101) fails, the switch (103) is turned on and the conventional UPS operates in so-called battery mode. When the conventional UPS operates in the battery mode, the battery (105) outputs DC power to the DC to DC converter (104). The DC to DC converter (104) raises voltage level of the DC power and outputs the raised voltage level DC power to the DC to AC converter (106) and the output filter device (107) to convert the DC power into an AC output power. The AC output power is then provided to the load. Therefore, the conventional UPS provides a continuous supply of electric power to the load. Furthermore, the conventional UPS further has a bypass output path (108) for protecting the conventional UPS.
However, in order to separate the line mode and the battery mode of the conventional UPS, the PFC and AC to DC converter (102) and the DC to DC converter (104) have to be disposed separately in the conventional UPS. Therefore, the cost of designing circuit of the conventional UPS is higher but the density of the power is lower.
To save the foregoing designing cost, some manufacturers designed an AC to DC and DC to DC converter that incorporates the AC to DC converter and the DC to DC converter. With reference to FIG. 11, the AC to DC and DC to DC converter (110) is electrically connected to a two-phase 3-wire input power supply and comprises four inductors (L11, L12, L21, L22), four semiconductor switches (S11, S12, S21, S22), four rectifying diodes (D111, D211, D121, D221) and two storing devices (C1, C2). When incorporating the AC to DC and DC to DC converter (110) in the conventional UPS, the UPS operates the AC to DC converting and DC to DC converting functions depending on what mode the UPS operates to control the semiconductor switches (S11, S12, S21, S22) on or off. Furthermore, the AC to DC and DC to DC converter may comprise six inductors, six semiconductor switches, six rectifying diodes and two storing capacitors when the AC to DC and DC to DC converter is electrically connected to a three-phase 4-wire input power supply.
However, such a AC to DC and DC to DC converter still requires using many semiconductor switches, and each semiconductor switch requires electrically connecting to an isolating driving circuit that controls the connected semiconductor switch. Therefore, how to reduce the amount of the semiconductor switches is a critical problem for the UPS manufacturers.
To overcome the shortcomings, the present invention provides a multi-input power converter and an UPS having the same to mitigate or obviate the aforementioned problems.